3d Printing Earrings in Blender
In this overview Chris Plush shows you some tips on prepping your 3d models in order to upload them to Shapeways.com for 3d printing. These techniques are also useful for other 3d printing sites such as 3dhubs.com.
Also check out the 3d print add-on which can be enabled in your user preferences which contains a few useful tools for 3d printing. You can find more info on the Blender wiki.